Prostate cancer is a significant worldwide health problem for which new treatments are needed. The goal of this research is to develop anti-prostate tumor vaccines as a treatment for cancer, and specifically prostate cancer. Our laboratory has been seeking to define appropriate antigens for inclusion in prostate cancer vaccines, target these antigens in rodent models using plasmid DNA vaccines, and ultimately to translate these findings to human clinical testing in patients with prostate cancer. We and other investigators have focused our initial efforts on prostatic acid phosphatase (PAP) as a prostate tumor vaccine antigen. We have previously demonstrated in rats that DNA vaccines encoding either human or rat PAP can elicit PAP-specific CD4+ and CD8+ T-cell responses, IFN? secreting responses, and antibody responses. Moreover, we have shown that CD4+ and CD8+ T-cells specific for PAP can be detected in patients with prostate cancer, suggesting that immunological tolerance to this protein can be circumvented in vivo in humans. We have also investigated a plasmid DNA vaccine encoding PAP in a dose-escalation phase I clinical trial in patients with recurrent non-metastatic prostate cancer. In that trial we observed no significant adverse events, demonstrated immunological efficacy in augmenting PAP-specific CD8+ T-cells, and observed an increase in PSA doubling time in several patients. Questions remain, however, as to the optimal frequency of immunization to maintain long-term effector and memory T-cell responses, and whether the development of these long-term responses will result in improved clinical outcomes. The goal of the current protocol will be to evaluate the safety and immunological efficacy of this same plasmid DNA vaccine, administered over a prolonged period of time with booster immunizations given at regular intervals or as defined by ongoing immune monitoring, to induce and/or augment CD8+ T-cell effector and memory immune responses to PAP in patients with castrate-resistant, non-metastatic prostate cancer. One cohort of subjects will be treated with six bi-weekly immunizations, as previously conducted, with immunizations continuing at regular 3-month intervals. The other cohort will be treated with six bi-weekly immunizations followed by booster immunizations at a schedule defined by the presence or absence of PAP-specific T-cell responses. This will be a small, randomized phase II trial design with fifteen subjects per cohort, powered to detect an immune response rate of 80% at one year after study initiation. The study design will permit an indirect comparison with our previous study with respect to immune response rates, and will have the goal of identifying an optimal approach for phase II clinical trial testing. Given that previous studies conducted by us and others have suggested that the induction of immune responses to PAP may be associated with clinical benefit in the treatment of prostate cancer, secondary endpoints will be to evaluate the effect on PSA doubling time and 1-year metastasis-free survival. The specific aims of the proposed clinical trial will be 1) to determine the safety of serial intradermal vaccinations of a DNA vaccine encoding PAP, with GM-CSF as a vaccine adjuvant, in patients with non-metastatic castrate-resistant prostate cancer;2) to determine whether PAP-specific IFN?-secreting CD8+ T-cells and long-term antigen-specific memory CD8+ T-cells can be elicited in patients with non-metastatic castrate-resistant prostate cancer by means of immunization with a plasmid DNA vaccine encoding PAP;and 3) to determine if antigen-specific effector and memory T-cells can be augmented by using individualized schedules of booster immunizations determined by immunological monitoring. PUBLIC HEALTH RELEVANCE: Prostate cancer is a significant worldwide health problem, and the second leading cause of cancer-related death in men in the United States. Patients with rising serum PSA after androgen deprivation therapy are at high risk for developing progressive, metastatic disease. The goal of this research is to develop effective anti-tumor DNA vaccines as a treatment for prostate cancer, and to specifically evaluate a vaccine in a clinical trial for patients with this stage of prostate cancer. Thus, this proposal is directly relevant to the mission of the National Cancer Institute, and directly relevant to this specific Program Announcement. In addition, the goal of this proposal is to determine if immune monitoring can be used to guide the ongoing schedule of treatment with a vaccine, to ultimately define an optimal schedule of treatment. This is consequently relevant to the development of other anti-tumor vaccines.